Accused Manhattan madam Anna Gristina pleaded guilty to promoting prostitution Tuesday and was assured she won't return to jail, ending with a whimper a case prosecutors once hoped would expose wealthy clients and law enforcement accomplices of a high-end sex-for-pay ring.

Gristina, 44, a mother from upstate Monroe, was held in jail on $2 million bail for four months as prosecutors tried to get her to spill the beans. But she refused, and they admitted they were never able to corroborate her alleged bragging about contacts in the NYPD, the FBI and the governor's office in Albany.

"We are left with a straightforward promoting prostitution case - a defendant who ran a brothel for many years and who profited from the sex trade," said Manhattan Assistant District Attorney Charles Linehan.

Gristina, released from jail in June after an appeals court ordered her bail reduced, pleaded guilty to her original indictment - setting up a sexual encounter between an undercover officer and two prostitutes in July 2011 - only after Judge Juan Merchan assured her that his planned sentence won't require her to return to Rikers Island.

"Your honor, I would gratefully like to accept the plea," Gristina said, ending a day of suspenseful speculation about a possible plea as her husband and children watched from the front row.

Gristina was first detained in February.

Prosecutors said she was arranging hookups at an apartment on East 78th and had been under investigation for five years.

Before imposing sentence, Merchan, the judge who originally imposed the $2 million bail, criticized Gristina for bringing her 9-year-old son to court. She faced up to seven years in prison. But despite his criticism and the sensational allegations, Merchan said that as a first offender Gristina deserved only six months in prison - which, with credits applied by correction officials, would be satisfied by the four months she has served - and five years' probation.

She will be sentenced in November. As a Scottish citizen, she may also face deportation.